While I dislike the facts, I understand the situation completely from a business perspective. Apple simply can’t keep investing in hardware that offers them so little return on investment. GPU drivers alone have proven to be too overwhelming for Apple, even when they still cared about towers. The numbers just aren’t there for Apple to justify continuing the development and support of hardware that accounts for such a negligible portion of their sales and profits. Xserve RAID and Xserve were perfect examples of this reality.
Things may have been different before the iPhone and iPad, when “high end” users still counted for something in terms of public mindshare (Hollywood credits, etc.) but clearly Apple no longer needs that kind of attention to be successful. Complex, expensive products purchased by a niche user base simply don’t figure prominently in Apple’s future.